1. Field of the Invention
The present invention relates to circuit modules, and, more particularly, to a circuit module in which a shielding layer disposed on a surface of an insulating layer covering an electronic component disposed on a substrate has a small thickness.
2. Description of the Related Art
In circuit modules in which an electronic component is disposed on a substrate and an insulating layer covers the electronic component, a shielding layer is sometimes formed on the surface of the insulating layer. Because of the shielding effect of the shielding layer, the electronic component disposed on the substrate is prevented from externally receiving electrostatic noise and failing to function normally, or is prevented from externally transmitting electrostatic noise.
Japanese Unexamined Patent Application Publication No. 2004-172176 discloses such a circuit module. FIG. 7 is a diagram illustrating a circuit module 300 disclosed in Japanese Unexamined Patent Application Publication No. 2004-172176.
The circuit module 300 includes a substrate 101. In the substrate 101, an inner conductive layer 102 and a via conductor 103 are formed. On one main surface of the substrate 101, a connection electrode 104 is formed. On the other main surface of the substrate 101, a terminal electrode 105 and a ground electrode 106 are formed. The connection electrode 104 and the inner conductive layer 102 are connected to each other through the via conductor 103, and the inner conductive layer 102 and the ground electrode 106 are connected to each other through the via conductor 103.
On one main surface of the substrate 101, a plurality of electronic components 107 are disposed. The electronic components 107 are connected via a predetermined wiring line (not illustrated) and form an electronic circuit. A predetermined portion of the electronic circuit extends to the terminal electrode 105 and the ground electrode 106.
On one main surface of the substrate 101, an insulating layer 108 made of a resin is formed so that it covers the electronic components 107. The insulating layer 108 is not formed on the entire main surface of one main surface of the substrate 101, and instead is only formed on a portion of one main surface of the substrate 101.
On the surface of the insulating layer 108, a shielding layer 109 is formed. For example, the shielding layer 109 is formed by molding a conductive resin.
In the circuit module 300 in the related art, however, a combined resistance generated by the shielding layer 109 and the inner conductive layer 102 is large. Accordingly, electrostatic noise externally received by the shielding layer 109 cannot be sufficiently grounded and an inner circuit may be affected by the electrostatic noise. In addition, electrostatic noise generated by the inner circuit in the circuit module 300 cannot be sufficiently grounded, and the electrostatic noise may be externally transmitted.